Proto-Indo-European root morphemes are characterised by co-occurrence constraints on stops, namely **TVT-, **C1VC1-, **DVD- and **TVDh. The traditional reconstruction and historical-linguistic...Show moreProto-Indo-European root morphemes are characterised by co-occurrence constraints on stops, namely **TVT-, **C1VC1-, **DVD- and **TVDh. The traditional reconstruction and historical-linguistic theories aiming to explain the root restrictions from historical-linguistic perspective are critically reviewed. Typology classifies the Proto-Indo-European root restrictions as absolute, static co-occurrence restrictions. **TVT and **C1VC1 are co-occurrence restrictions on place of articulation, whereas **DVD and **TVDh are co-occurrence restrictions on laryngeal features. The application of existing phonological theories shows that **TVT and **C1VC1 can be explained by the Obligatory Contour Principle. A model in Dispersion Theory explains **DVD as a dissimilatory constraint and **TVDh as the consequence of an assimilatory constraint on *Dh.Show less
